Do background processes get a SIGHUP when logging off?
- by Massimo
This is a followup to this question.
I've run some more tests; looks like it really doesn't matter if this is done at the physical console or via SSH, neither does this happen only with SCP; I also tested it with cat /dev/zero > /dev/null. The behaviour is exactly the same:
Start a process in the background using & (or put it in background after it's started using CTRL-Z and bg); this is done without using nohup.
Log off.
Log on again.
The process is still there, running happily, and is now a direct child of init.
I can confirm both SCP and CAT quits immediately if sent a SIGHUP; I tested this using kill -HUP.
So, it really looks like SIGHUP is not sent upon logoff, at least to background processes (can't test with a foreground one for obvious reasons).
This happened to me initially with the service console of VMware ESX 3.5 (which is based on RedHat), but I was able to replicate it exactly on CentOS 5.4.
The question is, again: shouldn't a SIGHUP be sent to processes, even if they're running in background, upon logging off? Why is this not happening?
Edit
I checked with strace, as per Kyle's answer.
As I was expecting, the process doesn't get any signal when logging off from the shell where it was launched. This happens both when using the server's console and via SSH.
